1. Technical Field
This invention is that of improved organic azo pigment compositions and processes for their preparation. The compositions of the invention have superior application properties including high gloss, improved transparency, high tinctorial strength and improved shade.
2. Background
Organic pigments are well known in the field of colorants. They are used in the coloring of printing inks, paints and plastics to impart a desired color in these articles. In addition, they find application to impart color to numerous other articles such as cosmetics, paper, leather, textile products etc.
An important class of organic pigments are the monoazo and disazo compounds derived from the coupling of compounds selected from the betanaphthols, the arylides, and the pyrazolones with a diazonium salt or a bisdiazonium salt of a substituted or unsubstituted aromatic amine or diamine. The preparation of such azo pigments is well known. An aromatic amine is typically diazotized in a strongly acidic aqueous medium with nitrous acid to form a diazotized derivative. The diazotized derivative is further reacted with a second molecule, a coupling component, to form the azo pigment. Numerous patents are available which describe the preparation of monoazo and disazo organic pigments; see e.g. U.S. Pat. Nos. 2,431,889; 3,617,171; 3,759,731; 3,775,148; 3,776,749; 4,341,701 and 4,968,352, the teachings of which are hereby incorporated by reference.
In addition to the chemical structure, the physical form of the pigment greatly influences its properties. Process conditions are controlled in the manufacturing process to influence such properties as crystalline form, particle size and particle size distribution to effect optimum dispersibility, tinctorial strength, gloss, transparency, shade and other properties.
It is also known in the art to add surface active agents, rosins and resins to the coupling reaction or after coupling to effect improved properties; see e.g. U.S. Pat. No. 4,968,352, Col. 7. It is the object of this invention to produce improved pigment compositions having superior properties by finishing the pigment composition in the presence of an insoluble metal salt of water or aqueous alkali soluble resin. The pigment compositions of this invention exhibit unexpectedly superior application properties in ink systems; e.g. improved gloss, transparency, tinctorial strength, brightness and dispersion stability.